The invention herein relates to electronic controls for monitoring pressures at various points in fluid circuitry for heavy, often specially constructed machinery such as multi-ton presses, engines for ocean-going cargo vessels or dynamometer assemblies for testing vehicle engines. In many instances, the machinery is integrated into the building or vessel where it is located. For example, a dynamometer assembly is known which has a dynamometer unit and associated gear boxes in the basement of a specially designed building to house the assembly, has a vehicle test stand located on the ground floor of the building, and has control rooms or like facilities located on a second floor or a mezzanine overlooking the test stand.
At least in the case of dynamometer assemblies, the heavy, specially constructed machinery represents an investment of hundreds of thousands or even millions of dollars. Failure to maintain pressure of coolants or liquid lubricants in the machinery could lead to expensive repairs or down time. If the machinery is integral to a building or vessel, the cost of removing major components or subassemblies and subsequently reinstalling them could be prohibitive. Consequently, it is logical for the pressure monitoring circuits to have some kind of redundancy to reduce the chance that a circuit failure will permit a fluid pressure failure to go unnoticed. One known form of redundancy is to have two pressure responsive switches at each point where pressure is monitored, one of the switches actuating when pressure drops to within a first pressure range and the other of the switches actuating in a second, lower pressure range.
Applicant's pressure controlling device is of the same general type as has been discussed above. Applicant's device has pairs of pressure responsive switches at various locations in fluid circuits of heavy machinery, and these switches send signals or responses to a monitoring circuit. Applicant's monitoring circuit reacts to the signals by selectively energizing or de-energizing indicator lights, by selectively outputing warning signals and by producing signals to initiate shutdown of part or all of the machinery. Applicant's monitoring circuit utilizes a novel, streamlined logic that reduces the amount of electrical power consumed by the circuit and speeds the operation of the circuit. In addition, applicant's circuit includes logic to indicate which of several low-pressure warning lights illuminates first. This logic is useful when monitoring several points in a fluid circuit which are communicated to one another. A pressure drop at one point in such a circuit is followed by pressure losses at the other points. Knowing which point experienced pressure failure first is often helpful in diagnosing the problem leading to the pressure failure.